The invention relates to a method for the control of a transmission in a vehicle having a service module actuable by a driver of the vehicle to select a desired gear, wherein the service module is connected to an automatic transmission control system which switches gears as a result of the driver""s actuation of the service module.
A method of this type is known from EP 0,670,440 B1 (corresponding to U.S. Pat. No. 5,425,689 which is incorporated herein by reference).
The known method serves to control a manually switchable, non-synchronized vehicle transmission of conventional design having a plurality of gears, which is operated in a partially automated manner by means of an electronic control system for the transmission (hereinafter referred to as a transmission control system), and by means of an electrical and pneumatic actuating system connected to same. Automation consists in that the mechanical movements required for a gear change are made by the electrical and pneumatic actuating system as a result of triggering signals from the transmission control system.
In a gear change controlled by the transmission control system, it is desirable for the gear change to be as rapid as possible in order to make full drive capacity available to the vehicle once more. Especially when changing gears in the direction of a higher gear ratio, i.e., when upshifting, the problem occurs that the relatively high engine rpm""s must be reduced to a suitable lower rotational speed suitable for engagement of the new gear with higher gear ratio. In order to speed up this process, according to the aforementioned prior art, an engine braking device is actuated when a gear is changed in the direction of a greater gear ratio, thereby contributing to a more rapid reduction of the engine rpm""s.
However, this method is not entirely satisfactory for speeding up gear engagement because engine braking devices of conventional design have a certain delay in response as they are switched on or off. This may result in an undesirably long actuating time for the engine braking device and therefore to an undesired lengthy gear changing process.
The present invention has as its object to propose a method for the control of a transmission which makes rapid gear changes possible through a more efficient utilization of an engine braking device.
A method for controlling a transmission of an engine-driven vehicle having a plurality of gears, the vehicle including a service module actuable by a driver of the vehicle to select a desired gear, the service module being connected to a transmission control system which automatically changes gears in response to actuation of the service module, said vehicle further including an engine braking system connected to said transmission control system which is actuable to brake the vehicle engine during a gear change, the method comprising: monitoring a transmission input rotational speed (NE) and a transmission output rotational output speed (NA) of the transmission; determining a synchronous rotational speed (NS) at which a gear change can be effected; actuating the engine braking system to reduce the transmission input rotational speed (NE) and synchronize it with the synchronous rotational speed (NS) so that the desired gear change can be effected; and disabling the engine braking system at a point in time before the expected synchronization of the rotational speeds (NE) and (NS) occurs. In one preferred embodiment, the engine braking system is disabled at a point in time when the difference between the transmission rotational input speed (NE) and the synchronous rotational speed (NS) becomes equal to or less than a predetermined rotational differential value. In another preferred embodiment, the engine braking system is disabled at a point in time which precedes the expected synchronization of the rotational speeds (NE, NS), by a fixed delay time (TA) which is typical for the engine braking system.
The invention has the advantage to be easily implemented without any need for employing additional sensors. The invention can be implemented simply by using sensors which are already present for a transmission control system and by simply adding a few program steps to the control program already running in the transmission control system.
In an advantageous further development of the invention, the vehicle acceleration or the vehicle deceleration is taken into account in determining the switch-off threshold of the engine braking device. This has the advantage that the invention can be used in a flexible manner with many different kinds of vehicle models and under different road conditions, for example, for mountain travel.
In another advantageous further development, the switch-off threshold following the switching off of the engine braking device is determined automatically by measuring the switch-off delay. This has the advantage that the switch-off threshold or the switch-off delay need not be determined separately for every vehicle by measurement to be then stored in the transmission control system.
It is a further advantage that as a result of the inventive method, influences which could lead to a modification of the typical value of the switch-off delay period, such as temperature influences, automatically lead to an adaptation of the switch-off threshold and thus further reduce the duration of a shifting process.